Cooling circuit and oil cooler

ABSTRACT

A cooling circuit includes a first coolant passage in which a coolant flows, a second coolant passage in which the coolant flows, a thermostat, and an oil cooler configured to heat or cool oil. The thermostat interrupts a flow of the coolant flowing through the first coolant passage when a temperature of the coolant flowing into the thermostat is lower than a predetermined temperature, and allows the coolant to flow through the first coolant passage when the temperature of the coolant is at or above a predetermined temperature. The oil cooler includes a first coolant inflow port, a first coolant outflow port, a second coolant inflow port, and a second coolant outflow port. The oil cooler heats or cools the oil by heat exchange between the coolant flowing from the first coolant inflow port or/and the second coolant inflow port and the oil.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of International Patent Application No. PCT/JP2018/043173 filed on Nov. 22, 2018, which designated the U.S. and claims the benefit of priority from Japanese Patent Applications No. 2017-245714 filed on Dec. 22, 2017. The entire disclosures of all of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a cooling circuit and an oil cooler.

BACKGROUND

An oil cooler of a cooling circuit includes a heat exchanger core in which multiple plates are laminated with each other.

SUMMARY

According to an aspect of the present disclosure, a cooling circuit may include a first coolant passage, a second coolant passage, a thermostat, and an oil cooler. The oil cooler includes a first coolant inflow port, a first coolant outflow port, a second coolant inflow port, and a second coolant outflow port. The thermostat may be configured to interrupt a flow of the coolant flowing through the first coolant passage when a temperature of coolant flowing into the thermostat is lower than a predetermined temperature, and to allow the coolant to flow through the first coolant passage and the second coolant passage, when the temperature of the coolant is equal to or more than a predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a schematic structure of a cooling circuit according to a first embodiment.

FIG. 2 is a view showing a cross-sectional structure of an oil cooler according to the first embodiment.

FIG. 3 is a perspective view showing a structure of an offset fin according to the first embodiment.

FIG. 4 is a block diagram showing an operation example of the cooling circuit according to the first embodiment.

FIG. 5 is a time chart showing changes in a coolant temperature of an engine and in an oil temperature of a transmission according to the first embodiment.

FIG. 6 is a block diagram showing an another operation example of the cooling circuit according to the first embodiment.

FIG. 7 is a block diagram showing a structure of a cooling circuit according to a second embodiment.

DETAILED DESCRIPTION

An oil cooler may include a heat exchanger core in which multiple plates are laminated with each other, and a passage control valve attached to a top portion of the heat exchanger core. The passage control valve may include a valve housing brazed to a top of the plates and a rotary valve. The passage control valve is provided with a low-temperature coolant inflow port through which coolant at a low temperature is supplied, a high-temperature coolant inflow port through which the coolant at a high temperature is supplied, and a coolant outflow port through which the coolant returns.

A coolant inflow port and a coolant outflow port of the heat exchanger core are configured to communicate with an interior of the valve housing.

The passages of the oil cooler appropriately communicate with each other in response to a rotational position of the rotary valve, so that oil is heated or cooled in the oil cooler.

In the oil cooler described above, a flow rate of the coolant used when the oil is heated is different from that used when the oil is cooled. More specifically, the flow rate of the low temperature coolant used to cool the oil tends to be larger than the flow rate of the high temperature coolant used to heat the oil.

In the oil cooler, the coolant is discharged from the single coolant outflow port, during the oil heating in which the flow rate of the coolant is relatively small, and during the oil cooling in which the flow rate of the coolant is relatively large. Therefore, a pressure loss of the coolant tends to be larger, in particular, during the oil cooling in which the flow rate of the coolant is relatively large.

If the pressure loss of the coolant becomes larger, the flow rate of the coolant is decreased, and thereby causing a reduction of heat exchange performance, an increase of a load of a pump, or the like.

The present disclosure is provided with an oil cooler and a cooling circuit configured to change a flow rate and reduce pressure loss, for example.

According to an exemplary embodiment of the present disclosure, a cooling circuit includes a first coolant passage in which a coolant flows, a second coolant passage in which the coolant flows, a thermostat, and an oil cooler configured to heat or cool oil. The thermostat is configured to interrupt a flow of the coolant flowing through the first coolant passage when a temperature of coolant flowing into the thermostat is lower than a predetermined temperature, and to allow the coolant to flow through the first coolant passage, when the temperature of the coolant is equal to or higher than a predetermined temperature.

For example, the oil cooler may include a first coolant inflow port, a first coolant outflow port, a second coolant inflow port, and a second coolant outflow port. The coolant flowing in the first coolant passage flows into the first coolant inflow port. The coolant flowing in the inner passage of the oil cooler flows out of the oil cooler through the first coolant outflow port, and returns the first coolant passage. The coolant flowing in the second coolant passage flows into the second coolant inflow port of the oil cooler. The coolant flowing into the oil cooler from the second coolant inflow port flows out of the oil cooler through the second coolant outflow port. The oil cooler is configured to heat or cool the oil by heat exchange between the coolant flowing from the first coolant inflow port or/and the second coolant inflow port and the oil.

For example, when the thermostat interrupts the flow of the coolant in the first coolant passage, only the coolant in the second coolant passage flows into the oil cooler. On the other hand, when the thermostat allows the coolant to flow through the first coolant passage, the coolant in both the first coolant passage and the second coolant passage flows into the oil cooler. Therefore, a flow rate of the coolant flowing in the oil cooler can be suitably changed.

In addition, the coolant is enabled to flow out from the oil cooler through both of the first coolant outflow port and the second coolant outflow port. Therefore, pressure loss of the coolant can be reduced, compared to an oil cooler which includes a single outflow port.

According to another exemplary embodiment of the present disclosure, an oil cooler is configured by a plurality of plates laminated to define an oil passage through which an oil flows and a coolant passage through which coolant flows, and the oil passage and the coolant passage are arranged alternatively. The oil cooler includes a plurality of coolant plates defining the coolant passage therein. The coolant plates define an inner passage in which the coolant flows, a first coolant inflow passage through which the coolant flows into the inner passage, a second coolant inflow passage through which the coolant flows into the inner passage, a first coolant outflow passage through which the coolant in the inner passage flows out, and a second coolant outflow passage through which the coolant in the inner passage flows out. The inner passage is configured to communicate with both the first coolant inflow passage and the second coolant inflow passage and to communicate with the first coolant outflow passage and the second coolant outflow passage, so that the coolant flows into the inner passage only through the second coolant inflow port when a flow of the coolant flowing into the first coolant inflow passage is closed, and the coolant flows into the inner passage through both of the first coolant inflow port and the second coolant inflow port when the coolant flows into the first coolant inflow passage and the second coolant inflow passage.

For example, when the coolant does not flow into the first coolant inflow passage, the coolant flows into the inner passage from only the second coolant inflow passage. On the other hand, when the coolant flows into the first coolant inflow passage, the coolant flows into the inner passage of the oil cooler from both the first coolant inflow passage and the second coolant inflow passage. Therefore, a flow rate of the coolant flowing through the inner passage can be suitably changed.

In addition, the coolant is enabled to flow out from the oil cooler through both of the first coolant outflow passage and the second coolant outflow passage. Therefore, the pressure loss of the coolant can be reduced in the oil cooler.

Embodiments of a cooling circuit and an oil cooler will be described with reference to the drawings as follows. The same reference numerals in the drawings are given to the same structures in order to eliminate explanation for easily understanding.

First Embodiment

A cooling circuit and an oil cooler according to a first embodiment will be described below.

FIG. 1 shows a cooling circuit 10 in the present embodiment. The cooling circuit 10 is equipped in a vehicle and includes an engine cooling circuit 20 in which coolant for an engine 40 circulates, and a transmission cooling circuit 30 in which hydraulic oil of a transmission 50 circulates. The engine cooling circuit 20 includes the engine 40, a radiator 41, a heater core 42, a thermostat 43, and a coolant pump 44.

A coolant passage W20 couples the engine 40 to the radiator 41. In addition, a coolant passage W21 couples the engine 40 to the heater core 42. Because of this, the coolant which has exchanged heat with the engine 40 is enabled to flow to at least one of the radiator 41 and the heater core 42 through the coolant passage W20 or/and the coolant passage W21.

In the present embodiment, the coolant passage W20 corresponds to a first coolant passage, and the coolant which flows in the coolant passage W20 corresponds to a first coolant.

The radiator 41 is configured to cool the coolant by heat exchange between the coolant which flows through an inside of the radiator 41 and air which flows through an outside of the radiator 41. The coolant cooled by the radiator 41 flows into the coolant pump 44 through a coolant passage W22.

The coolant pump 44 is a mechanical pump which is driven by power transferred from the engine 40 or an electric pump which is driven by electric power supplied from a battery equipped in the vehicle. The coolant pump 44 is configured to pressure-send the coolant flowing in the coolant pump 44 to the engine 40 and to circulate the coolant to components in the engine cooling circuit 20. The heater core 42 is an element of an air conditioner for a vehicle.

The heater core 42 is configured to perform the heat exchange between the coolant supplied from the engine 40 and the air flowing in an air conditioning duct of the air conditioner and to heat the air flowing in the air conditioning duct. The air conditioner heats a vehicle interior by a blowout of the heated air to the vehicle interior through the air conditioning duct. The coolant flowing out of the heater core 42 flows into the thermostat 43 through a coolant passage W23.

In the present embodiment, the coolant passage W23 corresponds to a second coolant passage, and the coolant which flows in the coolant passage W23 corresponds to a second coolant.

The thermostat 43 is provided at an intermediate location of the coolant passage W22 which couples the radiator 41 to the engine 40. When a coolant temperature is lower than a predetermined valve opening temperature Tth1, the thermostat 43 becomes a closed state and shuts off the coolant passage W22. The valve opening temperature Tth1 is set at, for example, 80 Celsius.

When the coolant temperature is lower than the valve opening temperature Tth1, the coolant is allowed to flow from the heater core 42 to the engine 40, while the coolant flowing from the radiator 41 to the engine 40 is interrupted.

When the coolant temperature is equal to or higher than the valve opening temperature Tth1, the thermostat 43 becomes in an open state, and the coolant passage W22 is opened. When the coolant temperature is equal to or higher than the valve opening temperature Tth1, the coolant is allowed to flow from the heater core 42 to the engine 40 and to flow from the radiator 41 to the engine 40.

When the coolant temperature becomes higher than a valve full-opening temperature Tth2 higher than the valve opening temperature Tth1, the thermostat 43 becomes a full-open state.

In the engine cooling circuit 20, when the coolant temperature is low such as in case of a cold start of the engine 40, the thermostat 43 becomes in the closed state. Because of this, the coolant pressure-sent by the coolant pump 44 is circulated through the engine 40 and the heater core 42, while bypassing the radiator 41.

In this case, because the radiator 41 does not cool the coolant, the coolant temperature is easily raised for a short time period. As a result, the engine 40 and the heater core 42 can be easily warmed for a short time.

Subsequently, when the coolant temperature is raised to or above the valve opening temperature Tth1, the thermostat 43 becomes in the open state. Thus, the coolant pressure-sent by the coolant pump 44 is circulated through the engine 40, the radiator 41, and the heater core 42.

Because of this, the coolant cooled by the radiator 41 is supplied to the engine 40, and the engine 40 is cooled by the heat exchange with the coolant. A part of the coolant heated by the engine 40 is supplied to the heater core 42, and the heater core 42 is maintained in high temperature. Therefore, the heater core 42 is enabled to heat the air which flows in the air conditioning duct.

The transmission cooling circuit 30 includes the transmission 50, an oil cooler 51, and an oil pump 52. An oil passage W30 couples the transmission 50 to an oil inflow port 510 a of the oil cooler 51. The oil flowing out of the transmission 50 flows into the oil inflow port 510 a of the oil cooler 51 through the oil passage W30.

The oil cooler 51 includes the oil inflow port 510 a, a first coolant inflow port 511 a, a second coolant inflow port 512 a, an oil outflow port 510 b, a first coolant outflow port 511 b, and a second coolant outflow port 512 b. The oil flowing into the oil inflow port 510 a flows in the oil cooler 51 and is discharged from the oil outflow port 510 b. The oil discharged from the oil outflow port 510 b flows into the oil pump 52 through an oil passage W31.

The oil pump 52 is, for example, an electric pump driven by the electric power supplied from a battery equipped in the vehicle. The oil pump 52 is configured to pump and pressure-send the oil to the transmission 50 and to circulate the oil through components in the transmission cooling circuit 30.

A bypass passage W40 couples the first coolant inflow port 511 a of the oil cooler 51 to the coolant passage W20. Because of this, a part of the coolant flowing in the coolant passage W20, that is, a part of the coolant discharged from the engine 40 flows into the oil cooler 51 through the bypass passage W40.

A check valve 45 is disposed at an intermediate location in the bypass passage W40. The check valve 45 is configured to allow the coolant to flow from the coolant passage W20 toward the first coolant inflow port 511 a, while preventing the flow of the coolant from the first coolant inflow port 511 a toward the coolant passage W20. In the present embodiment, the check valve 45 corresponds to a flow controller.

A bypass passage W41 couples the second coolant inflow port 512 a of the oil cooler 51 to the coolant passage W23. Because of this, a part of the coolant flowing in the coolant passage W23, that is, a part of the coolant discharged from the heater core 42, flows into the oil cooler 51 through the bypass passage W41.

The coolant flowing into the oil cooler 51 from at least one of the first coolant inflow port 511 a and the second coolant inflow port 512 a exchanges the heat with the oil flowing in the oil cooler 51. Therefore, the oil is heated or cooled in the oil cooler 51. The coolant flowing through the oil cooler 51 is discharged from the first coolant outflow port 511 b or the second coolant outflow port 512 b.

A bypass passage W42 couples the first coolant outflow port 511 b to the coolant passage W20 at a downstream side of a connection portion at which the coolant passage W20 is connected to the bypass passage W40. Therefore, the coolant discharged from the first coolant outflow port 511 b flows into the coolant passage W20 through the bypass passage W42.

A bypass passage W43 couples the second coolant outflow port 512 b to the coolant passage W23 at a downstream side of a connection portion at which the coolant passage W23 is connected to the bypass passage W41. Therefore, the coolant discharged from the second coolant outflow port 512 b flows into the coolant passage W23 after being heat exchanged with the oil in the oil cooler 51.

A detailed structure of the oil cooler 51 will be described below.

Multiple plates are laminated in the oil cooler 51 such that the oil passage through which the oil flows and the coolant passage through which the coolant flows are arranged alternatively.

FIG. 2 shows a cross-sectional structure of a coolant plate 70 which forms the coolant passage of the oil cooler 51. As shown in FIG. 2, the cross-sectional structure of each coolant plate 70 has approximately a hexagon shape in a section perpendicular to a lamination direction in which the plates are laminated. An inner passage 77 is formed in the coolant plate 70, and the coolant flows in the inner passage 77. The coolant plate 70 includes a first coolant inflow passage 72 a, a second coolant inflow passage 73 a, a first coolant outflow passage 72 b, and a second coolant outflow passage 73 b, which are provided to communicate with the inner passage 77.

The coolant plate 70 further includes an oil inflow passage 71 a and an oil outflow passage 71 b which are not connected to the inner passage 77. That is, the oil inflow passage 71 a and the oil outflow passage 71 b are separated from the inner passage 77. The first coolant inflow passage 72 a is provided at a corner C1 of the coolant plate 70. Two corners C2, C3 are located adjacent to the corner C1 in the coolant plate 70. The oil outflow passage 71 b and the second coolant inflow passage 73 a are provided at the corner C2 and the corner C3, respectively.

Corners C4 to C6 are formed at diagonal positions of the corners C1 to C3, respectively, in the coolant plate 70. The first coolant outflow passage 72 b, the oil inflow passage 71 a, and the second coolant outflow passage 73 b are provided at the corner C4, the corner C5, and the corner C6, respectively.

An internal diameter of the first coolant inflow passage 72 a is larger than an internal diameter of the second coolant inflow passage 73 a. Similarly, an internal diameter of the first coolant outflow passage 72 b is larger than an internal diameter of the second coolant outflow passage 73 b.

Hereinafter, a direction from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b is referred to as X direction, while a direction perpendicular to the X direction is referred to as Y direction, as shown in FIG. 2. In addition, a direction from the second coolant inflow passage 73 a toward the second coolant outflow passage 73 b, that is, a direction in which an angle between the X direction and the Y direction is bisected is referred to as a direction.

In the present embodiment, the X direction corresponds to a first direction, the Y direction corresponds to a second direction, and the a direction corresponds to a third direction. An offset fin 74 is disposed at the coolant inner passage 77 of the coolant plate 70. As shown in FIG. 3, the offset fin 74 includes multiple cut-and-raised parts 740 in the X direction. Each cut-and-raised part 740 is formed by cutting and raising a plate partially. The offset fin 74 is opened in the X direction. The cut-and-raised parts 740, 740 adjacent to each other in the X direction are offset in the Y direction.

In the offset fin 74, when the coolant flows in the X direction shown in FIG. 2, that is, when the coolant flows from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b, the coolant flows in the cut-and-raised part 740 and through a clearance between the cut-and-raised parts 740, 740 adjacent to each other. Therefore, a flow resistance against the coolant is small.

On the other hand, when the coolant flows in the a direction, that is, when the coolant flows from the second coolant inflow passage 73 a toward the second coolant outflow passage 73 b, the coolant tends to collide to the cut-and-raised part 740, and the flow resistance against the coolant becomes larger. In the present embodiment, the offset fin 74 corresponds to a flow resistance applying part configured to apply a flow resistance to a fluid.

A rib 75 is located between the first coolant inflow passage 72 a and the second coolant inflow passage 73 a at the coolant plate 70 and extends from an inner wall of the coolant plate 70 to an inside. The rib 75 is disposed to restrict the coolant from flowing through a shortcut circuit between the first coolant inflow passage 72 a and the second coolant inflow passage 73 a.

A rib 76 is located between the first coolant outflow passage 72 b and the second coolant outflow passage 73 b at the coolant plate 70 and extends from the inner wall of the coolant plate 70 to an inside. The rib 76 restricts the coolant from flowing through the shortcut circuit between the first coolant outflow passage 72 b and the second coolant outflow passage 73 b.

In the oil cooler 51, the oil flows from the oil inflow port 510 a shown in FIG. 1 into the oil inflow passage 71 a shown in FIG. 2. The oil flowing into the oil inflow passage 71 a flows into an oil inner passage formed in an oil plate which is adjacent to the coolant plate 70. The oil flowing in the oil inner passage flows in a direction shown by an arrow D1 in FIG. 2. The oil flows in a flow direction D1 that intersects with a flow direction D2 of the coolant which flows from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b. The oil flowing into the oil inner passage is discharged from the oil outflow port 510 b shown in FIG. 1 through the oil outflow passage 71 b.

Next, operation examples of the cooling circuit 10 and the oil cooler 51 in the present embodiment will be described below.

When the temperature of the coolant flowing in the engine cooling circuit 20 is lower than the valve opening temperature Tth1, such as in the cold start of the engine 40, the thermostat 43 is in the closed state.

In this case, as shown by a thick line in FIG. 4, the coolant circulates through the engine cooling circuit 20. That is, the coolant circulates through the engine 40, the heater core 42, the oil cooler 51, the thermostat 43, and the coolant pump 44, while does not circulate through the radiator 41. In this case, the coolant heated by the heat exchange with the engine 40 flows into the second coolant inflow port 512 a of the oil cooler 51 through the coolant passage W21, the heater core 42, the coolant passage W23 and the bypass passage W41 in this order, and flows in the coolant inner passage 77 of the oil cooler 51.

The oil is heated by the heat exchange between the coolant flowing in the coolant inner passage 77 of the oil cooler 51 and the oil flowing in the oil inner passage. Thus, the oil flowing in the transmission 50 can be heated.

The coolant in which the temperature is reduced by the heat exchange with the oil is discharged to the bypass passage W43 through the second coolant outflow passage 73 b and the second coolant outflow port 512 b. The coolant discharged to the bypass passage W43 is heated again by flowing into the engine 40 through the coolant passage W23, the thermostat 43, and the coolant pump 44.

In the oil cooler 51, the coolant flows from the second coolant inflow passage 73 a toward the second coolant outflow passage 73 b and tends to receive the flow resistance from the offset fin 74. Therefore, a flow rate of the coolant which flows in the oil cooler 51 is reduced.

As shown in FIG. 5, for example, when the operation of the engine 40 starts at a time t10, a coolant temperature Te of the engine 40 is increased for a shorter period, compared to an oil temperature Tt of the transmission 50. Thereby, a temperature difference ΔT between the coolant temperature Te of the engine 40 and the oil temperature Tt of the transmission 50 becomes larger, and the oil can be heated even in a case where the flow rate of the coolant flowing in the oil cooler 51 is low.

Subsequently, when the temperature of the coolant flowing in the engine coolant circuit 20 is increased to or above the valve opening temperature Tth1, the thermostat 43 becomes in the valve open state. In this state, the coolant circulates through the engine coolant circuit 20 as shown by a thick line in FIG. 6. That is, the coolant can circulate through the all components in the engine coolant circuit 20 in FIG. 6.

In this case, the coolant cooled at the radiator 41 flows into the first coolant inflow port 511 a of the oil cooler 51 through the engine 40, the coolant passage W20, and the bypass passage W40.

In addition, the coolant flowing in the coolant passage W23 flows into the second coolant inflow port 512 a of the oil cooler 51 through the bypass passage W41. The coolant flowing into the first coolant inflow port 511 a and the coolant flowing into the second coolant inflow port 512 a flow through the coolant inner passage 77 of the oil cooler 51, respectively.

Thus, the oil is cooled by the heat exchange between the coolant flowing in the coolant inner passage 77 and the oil flowing in the oil inner passage in the oil cooler 51. That is, the oil flowing in the transmission 50 is cooled.

As shown in FIG. 5, the oil temperature Tt of the transmission 50 is reduced, at a time t11 at which the coolant temperature exceeds the valve opening temperature Tth1 and thereafter.

The coolant heated by the heat exchange with the oil is discharged to the bypass passage W42 through the first coolant inflow passage 72 a and the first coolant outflow port 511 b or to the bypass passage W43 through the second coolant outflow passage 73 b and the second coolant outflow port 512 b.

The coolant discharged to the bypass passage W42 flows into the radiator 41 through the coolant passage W20 and is cooled again in the radiator 41.

In the cooling circuit 10 and the oil cooler 51 of the present embodiments described above, operational effects shown by (1) to (6) can be obtained.

(1) When the thermostat 43 interrupts the flow of the coolant in the coolant passage W20, the coolant does not flow into the first coolant inflow passage 72 a of the oil cooler 51 and flows into the inner passage 77 of the oil cooler 51 through only the second coolant inflow passage 73 a. On the other hand, when the thermostat 43 allows the coolant to flow through the coolant passage W20, the coolant flows into the inner passage 77 of the oil cooler 51 through the first coolant inflow passage 72 a and the second coolant inflow passage 73 a.

Therefore, the flow rate of the coolant flowing in the oil cooler 51 can be changed. In addition, the coolant is enabled to flow out from the oil cooler 51 through the first coolant outflow port 511 b and the second coolant outflow port 512 b and through the first coolant outflow passage 72 b and the second coolant outflow passage 73 b. Therefore, the pressure loss of the coolant can be effectively reduced, compared to a known oil cooler which includes a single outflow port and a single outflow passage.

(2) The check valve 45 is provided in the bypass passage W40 which couples the first coolant inflow port 511 a of the oil cooler 51 to the coolant passage W20. The check valve 45 is configured to check and regulate the flow of the coolant from the first coolant inflow port 511 a of the oil cooler 51 toward the coolant passage W20.

Because of this, when the thermostat 43 is in the closed state, a reverse flow of the coolant from the inner passage 77 of the oil cooler 51 toward the coolant passage W20 can be prevented.

(3) In the oil cooler 51, the coolant flowing into the first coolant inflow passage 72 a from the first coolant inflow port 511 a is discharged from the first coolant outflow port 511 b through the first coolant outflow passage 72 b.

The coolant flows in the flow direction D2 that intersects with the flow direction D1 of the oil in the oil cooler 51. Therefore, the heat exchange between the coolant and the oil can be performed more efficiently, and a cooling efficiency of the oil can be enhanced.

(4) The coolant plate 70 of the oil cooler 51 includes the offset fins 74. The offset fins 74 are configured to cause a flow resistance against the coolant when the coolant flows in the X direction from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b to be different from a flow resistance against the coolant when the coolant flows in the a direction from the second coolant inflow passage 73 a toward the second coolant outflow passage 73 b.

More specifically, the flow resistance of the coolant flowing in the a direction from the second coolant inflow passage 73 a toward the second coolant outflow passage 73 b is larger than the flow resistance of the coolant flowing in the X direction from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b. Therefore, the coolant tends to flow from the first coolant inflow passage 72 a toward the first coolant outflow passage 72 b, and the coolant in the oil cooler 51 tends to flow to the radiator 41. As a result, the coolant in the cooling circuit 10 can be cooled more easily, and the cooling efficiency of the cooling circuit 10 can be enhanced.

In addition, the difference between the flow resistances in two directions can be caused easily by an arrangement of the offset fin 74 in the coolant plate 70.

(5) In the oil cooler 51, the first coolant inflow passage 72 a is located opposite to the first coolant outflow passage 72 b with respect to the offset fins 74 in the X direction. In addition, the second coolant inflow passage 73 a is located to the second coolant outflow passage 73 b with respect to the offset fins in the a direction. Therefore, while high heat exchange efficiency between the coolant and the oil can be maintained, the flow resistance of the coolant flowing in the X direction can be kept different from the flow resistance of the coolant flowing in the a direction.

(6) The rib 75 is provided between the first coolant inflow passage 72 a and the second coolant inflow passage 73 a in the oil cooler 51. The rib 75 enables to restrict the coolant flowing in the shortcut between the first coolant inflow passage 72 a and the second coolant inflow passage 73 a, and a reduction of heat exchange performance of the oil cooler 51 can be restricted.

Second Embodiment

Next, a cooling circuit 10 in a second embodiment will be described. In the second embodiment, difference parts with the cooling circuit 10 in the first embodiment will be mainly described below. The engine 40 in the present embodiment is an engine with a supercharger.

As shown in FIG. 7, the cooling circuit 10 in the present embodiment includes a CAC cooling circuit 80 through which a coolant from a charge air cooler (CAC) 81 circulates, instead of the circuit which includes the heater core 42 described in the first embodiment. The CAC cooling circuit 80 includes the CAC 81, a low temperature coolant radiator 82, a coolant pump 83, and a thermostat 84.

The CAC 81 is configured to raise air density by cooling intake air compressed by a supercharged engine 40. The coolant circulates between the CAC 81 and the low temperature coolant radiator 82 through coolant passages W50, W51.

The low temperature coolant radiator 82 is configured to cool the coolant by heat exchange between the coolant flowing in the low temperature coolant radiator 82 and air flowing outside of the low temperature coolant radiator 82. The coolant pump 83 is provided in the coolant passage W51. The coolant pump 83 is configured to circulate the coolant in the CAC cooling circuit 80.

A coolant passage W52 couples the second coolant inflow port 512 a of the oil cooler 51 to the coolant passage W50. In addition, a coolant passage W53 couples the second coolant outflow port 512 b of the oil cooler 51 to the coolant passage W51.

In the present embodiment, the coolant passage W52 corresponds to the second coolant passage, and the coolant flowing in the coolant passage W52 corresponds to the second coolant.

The thermostat 84 is located at a position at which the coolant passage W50 is connected to the coolant passage W52. The thermostat 84 is configured to become in a closed state when the coolant temperature is lower than a predetermined temperature and to interrupt the coolant flow in the coolant passage W50.

On the other hand, the thermostat 84 is configured to become in an opened state when the coolant temperature is at or above a predetermined temperature and to allow the coolant to flow through the coolant passage W50 when the thermostat 84 is in the opened state.

In the cooling circuit 10 of the present embodiment, a cooling circuit W24 couples the coolant passage W20 to the coolant passage W22. The cooling circuit W24 is a passage through which the coolant flowing in the coolant passage W20 bypasses the radiator 41 and flows to the coolant passage W22.

According to the structure described above, when the thermostats 43, 84 are in the closed state, the coolant which has been heated by the heat exchange at the CAC 81 is supplied to the oil cooler 51. Therefore, the oil cooler 51 enables to heat the oil by the heat exchange between the coolant and the oil.

Other Embodiments

Embodiments may be suitably modified to have structures described below. For example, an electromagnetic valve may be provided in the bypass passage W40 as a flow controller which regulates the flow of the coolant, instead of the check valve 45. The oil cooled by the oil cooler 51 is not limited to the oil used for the transmission 50 and may be oil used for a power machine such as the engine 40.

The cooling circuit 10 may cool an electromotor equipped in the vehicle, an inverter to drive the electromotor, or the like, instead of the engine 40. The coolant plate 70 may include a suitable structure other than the offset fins as the flow resistance applying part. The present disclosure is not limited by above examples.

The present disclosure encompasses various variations and modifications to above examples including features of the present disclosure, even if a skilled person modifies. The present disclosure is not limited by the elements, the locations, the conditions, the shapes or the like in above examples and can be modified. Each elements in the examples may be combined suitably except for a case where a technical inconsistency occurs. 

What is claimed is:
 1. A cooling circuit comprising: a first coolant passage in which a coolant flows; a second coolant passage in which the coolant flows; a thermostat configured to interrupt a flow of the coolant flowing through the first coolant passage when a temperature of coolant flowing into the thermostat is lower than a predetermined temperature, and to allow the coolant to flow through the first coolant passage when the temperature of the coolant is at or above a predetermined temperature; and an oil cooler configured to heat or cool oil, wherein the oil cooler includes: a first coolant inflow port into which the coolant flowing in the first coolant passage flows; a second coolant inflow port into which the coolant flowing in the second coolant passage flows; an inner passage provided therein to communicate with the first coolant inflow port and the second coolant inflow port; a first coolant outflow port, provided to communicate with the inner passage, through which the coolant having passed through the inner passage flows out of the oil cooler and flows into the first coolant passage; and a second coolant outflow port, provided to communicate with the inner passage, through which the coolant having passed through the inner passage flows into the second coolant passage, the inner passage of the oil cooler is configured to perform heat exchange between the coolant flowing therein and the oil, and the first coolant passage and the second coolant passage are coupled to the oil cooler, to cause the coolant in the second coolant passage flows into the inner passage only through the second coolant inflow port when the thermostat interrupts the flow of the coolant flowing through the first coolant passage, and to cause the coolant in the first coolant passage and the second coolant passage flows into the inner passage through both of the first coolant inflow port and the second coolant inflow port when the thermostat allows the flow of the coolant flowing through the first coolant passage.
 2. The cooling circuit according to claim 1 further comprising: a bypass passage that couples the first coolant inflow port to the first coolant passage; and a flow regulator provided in the bypass passage and configured to regulate a flow of the coolant flowing from the first coolant inflow port toward the first coolant passage.
 3. The cooling circuit according to claim 2, wherein the flow regulator is a check valve.
 4. The cooling circuit according to claim 1, wherein the oil cooler is configured to have a flow direction of the coolant flowing from the first coolant inflow port to the first coolant outflow port, which intersects with a flow direction of the oil flowing in the oil cooler.
 5. The cooling circuit according to claim 1, wherein the oil is used for an transmission in a vehicle.
 6. The cooling circuit according to claim 1, wherein the oil is used for a power machine in a vehicle.
 7. An oil cooler configured by a plurality of plates laminated to define an oil passage through which an oil flows and a coolant passage through which coolant flows, the oil passage and the coolant passage being arranged alternatively, the oil cooler comprising a plurality of coolant plates defining the coolant passage, each of the coolant plate includes: an inner passage in which the coolant flows; a first coolant inflow passage through which the coolant flows into the inner passage; a second coolant inflow passage through which the coolant flows into the inner passage; a first coolant outflow passage through which the coolant in the inner passage flows out; and a second coolant outflow passage through which the coolant in the inner passage flows out, the inner passage is configured to communicate with both the first coolant inflow passage and the second coolant inflow passage and to communicate with the first coolant outflow passage and the second coolant outflow passage, to cause the coolant flows into the inner passage only through the second coolant inflow port when a flow of the coolant flowing into the first coolant inflow passage is closed, and to cause the coolant flows into the inner passage through both of the first coolant inflow port and the second coolant inflow port when the coolant flows into the first coolant inflow passage and the second coolant inflow passage.
 8. The oil cooler according to claim 7, wherein the coolant plate further includes a flow resistance applying part configured to cause a flow resistance of the coolant flowing in a first direction from the first coolant inflow passage toward the first coolant outflow passage to be different from a flow resistance of the coolant flowing in a second direction from the second coolant inflow passage toward the second coolant outflow passage.
 9. The oil cooler according to claim 8, wherein the flow resistance applying part is an offset fin that includes a plurality of cut-and-raised parts, formed by cutting and raising a plate partially and lined in the first direction, and the cut-and-raised parts adjacent to each other in the first direction are offset from each other.
 10. The oil cooler according to claim 8, wherein the cut-and-raised parts adjacent to each other in the first direction are offset in the second direction that is perpendicular to the first direction, the first coolant inflow passage is located opposite to the first coolant outflow passage in the first direction with respect to the offset fin, and the second coolant inflow passage is located at an opposite side of the second coolant outflow passage with respect to the offset fin in a third direction that bisects an angle between the first direction and the second direction.
 11. The oil cooler according to claim 7, further comprising a rib provided between the first coolant inflow passage and the second coolant inflow passage to restrict the coolant from flowing in shortcut between the first coolant inflow passage and the second coolant inflow passage.
 12. The oil cooler according to claim 7, wherein the second coolant inflow passage causes the coolant to flow toward the second coolant outflow passage in a direction that intersects with a flow direction of the oil. 